1. Field of the Invention
The present invention relates to the separation of enantiomers.
2. Description of the Prior Art
Enantiomers are mirror-image isomers of the same compound with identical physical properties except that they rotate the plane of polarized light in opposite directions. Enantiomers also have identical chemical properties except toward chiral (optically active) reagents.
Chromatographic resolution of optical isomers requires the introduction of an asymmetric environment either intramolecularly, by conversion to diastereomers, or intermolecularly, by the use of chiral stationary or mobile phases. In gas chromatography, excellent resolution of derivatized amino acids has been achieved via diastereomers (R. Charles, G. Fischer, E. Gil-av, Israel J. Chem. 1, 234 (1963); G. E. Pollock, V. I. Oyama, R. D. Johnson, J. Gas Chromatogr. 3, 174 (1965)), as well as with chiral stationary phases. N-lauroyl-L-valine t-butylamide is an example of a useful chiral stationary phase. (B. Feibush, Chem. Commun. 544 (1971); R. Charles, U. Beitler, B. Fiebush, E. Gil-Av, J. Chromatogr. 112, 121 (1975). See also H. Frank, G. J. Nicholson, E. Bayer, J. Chromatogr. Sci. 15, 174 (1977).) Similarly in liquid chromatography, both these approaches have led to good separations, e.g. of diastereomeric dipeptides (J. M. Manning and S. Moore J. Biol. Chem. 243, 5591 (1968); F. Mikes, G. Boshart, E. Gil-Av, J. Chromatogr. 112,205 (1976)); and H. Numan, R. Helder, H. Wynberg,) Recueil 95, 211 (1976)) have resolved helicenes on optically active supports.
In contrast, the effect of chiral eluants has not been extensively investigated and has been described in only a few publications e.g.; W. H. Pirkle and D. L. Sikkenga, J. Chromatogr. 123, 400 (1976); and H. Nakazawa and H. Yoneda, ibid. 160, 89 (1978) and references therein. Le Page et al. (Anal. Chem. 51:433 (1979)) have recently separated dansyl derivatives of amino acids by reverse phase liquid chromotography using a chiral eluant. They use a chiral diethylenetriamine ligand coordinated to zinc dissolved in the eluant and have shown the separation of several pairs of derivatized enantiomers. In contrast, in the present system it is unnecessary to derivatize the enantiomers.